Gas and oil wells often produce fluids containing particulates which cause premature failures in piping. A wellhead conducts a fluid flow stream through equipment including chokes and metering apparatus. Particulates such as sand can be produced from the gas or oil formation itself or, in many cases, or introduced sand such as fracturing sand being recovered after stimulation operations. If desanding apparatus is not used, or not used long enough, upon initiating production, the sand concentration though downstream production piping causes accelerated degradation. The placement and orientation of various equipment can result in the occasional bend, including right angle or 90 degree elbows. The elbows result in a change in direction and marked increase in the erosive effect of contained particulates. When flow direction is changed in the bend, the particulates do not parallel the fluid flow, but resist a trajectory change and move against the outside of the turn, eroding the contact points. The erosions patterns in bends, tees, and blind tee connections can be complex, the ultimate point of failure from erosion being somewhat un-predictable.
Internal erosion of the piping is not readily detected until failure and failure can be catastrophic, the fluid flow such as gas being under pressure, flammable and often containing H2S which is fatal in even low concentrations. This establishes the need for a effective device.
One prior art early warning device is that disclosed in U.S. Pat. No. 7,246,825, which provides an elbow in a block having a main fluid passageway. The block further contains a matrix of passageways, separated from the main passageway by sufficient wall material that expected erosion to destruction will occur only over a reasonable operations period. The matrix of passageways is maintained at a low and differential pressure to that of the main flow stream. Erosion eventually breaks through the wall material, connecting the flow with the matrix of passageways. The matrix pressure is monitored and when the differential pressure climbs to the pressure in the process stream, breakthrough is detected and an orderly turnaround can be scheduled for replacement of the block. The matrix is rated for the process pressure. One shortcoming is that the matrix of holes have to intersect the area that was being eroded, being an uncertain science. The matrix cannot provide 100% coverage as the holes are inside the pressure boundary.
Another form of prior art apparatus includes ceramic lined pipes and machined ceramic elbows.
The ceramic material of the elbow forms part of the pressure boundary and is therefore required to have sufficient tensile strength to meet the pressure requirements. This requires special ceramics or overly thick material. As well, some regulatory codes would require special exemptions to use this material.